The invention relates to a gas and steam turbine system for generating electricity. The system has a steam generator generating steam for a steam turbine, which is heated by an exhaust gas from a gas turbine, and a cooling device for cooling combustion air for a gas turbine.
As systems for generating electricity have been developed, the systems have become ever more complex in order to achieve higher efficiencies. Thus, in gas and steam turbine systems, steam generators and associated steam turbines having two or more compression stages are normally positioned downstream from the gas turbine. In the process, a fresh steam condition of about 150 bars at a temperature of more than 535xc2x0 C. is aimed for at a high-pressure stage.
Such systems achieve a high system efficiency of about 57 to 58%. The complexity required for this purpose for the configuration of the system and for its operation has, however, limited the use of such systems, for financial reasons, to systems with relatively high power output ratings. The high level of complexity for system construction has in this case resulted in particular from the use of special materials, which are generally expensive, and required to withstand the temperature and pressure stresses. Furthermore, the need to specify tighter tolerances for the temperature and pressure levels has resulted in a comparatively high maintenance effort, with the maintenance personnel requiring a particularly high training level to satisfy these requirements.
Published, Non-Prosecuted German Patent Application DE 199 24 067.1 proposes that the combustion air for gas turbines be cooled. For this purpose, in addition to being cooled, the combustion air is also dried and rehumidified in a complex device, so that the hardware complexity and the system maintenance effort are particularly high.
It is accordingly an object of the invention to provide a gas and steam turbine system which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which is used for medium and low ratings with normal complexity, achieves particularly high efficiency and, at the same time, places only average requirements on the maintenance personnel.
With the foregoing and other objects in view there is provided, in accordance with the invention, a gas and steam turbine system for generating electricity. The system includes a gas turbine producing an exhaust gas, a steam generator that receives and is heated by the exhaust gas from the gas turbine, and a steam turbine that is connected to the steam generator and only has a medium-pressure section and a low-pressure section. A cooling and compressing device receives combustion air and is connected to and supplies the combustion air to the gas turbine. The cooling and compressing device has at least two stages for compressing the combustion air, the combustion air being cooled after at least one of the two stages in the cooling and compressing device. An air preheater is connected to the cooling and compressing device for heating the combustion air at least after a last of the two stages of the cooling and compressing device.
The object is achieved according to the invention in that the combustion air can be compressed in at least two stages, being cooled after at least one stage, and with the capability to be heated at least after the last stage of the compressor.
In this case, the steam turbine has only a medium-pressure section and a low-pressure section.
These measures reduce the system complexity for the steam turbine to about two thirds of the complexity required for a conventional gas and steam turbine system and, increase the rating of the gas turbine by reducing the compression power.
Omitting the high-pressure turbine achieves a considerable cost advantage in terms of the production costs for the gas and steam turbine system. Cooling and heating the combustion air in two stages reduces the power consumption, in particular the compressor power consumption, and at the same time increases both the gas turbine power and its efficiency. Overall, the system concept according to the invention for a gas and steam turbine system results in an efficiency comparable with known systems, while resulting in considerably reduced financial costs.
The combustion air is advantageously cooled using boiler supply water of a medium-pressure steam generator in at least one air/water heat exchanger. The combustion air is expediently heated, before entering the combustion chamber, in an air preheater by the exhaust gas from the gas turbine.
In accordance with an added feature of the invention, a combustion chamber is provided that is connected between the air preheater and the gas turbine. The air preheater is connected to and receives the exhaust gas from the gas turbine, and the combustion air is heated before entering the combustion chamber in the air preheater by the exhaust gas from the gas turbine.
In accordance with another feature of the invention, the steam generator includes a medium-pressure steam generator generating superheated steam that is supplied to the steam turbine, and a low-pressure steam generator generating further superheated steam that is also supplied to the steam turbine.
In this case, the rating of the gas turbine may be approximately equal to three-times the rating of the steam turbine to which superheated steam is applied from a medium-pressure steam generator and from a low-pressure steam generator.
It is expedient to split condensation emerging from a condenser, which is positioned downstream from the steam turbine, into two flow elements of approximately equal magnitude, one of which can be supplied to the medium-pressure section and the other to the low-pressure section of the steam generator.
The steam emerging from the medium-pressure turbine can be combined, either with or without intermediate superheating, with the steam coming from the low-pressure section of the steam generator, and supplied to the low-pressure turbine.
In the medium-pressure steam generator and the low-pressure steam generator, the exhaust gas from the gas turbine can successively heat a medium-pressure superheater, a low-pressure superheater, a medium-pressure vaporizer, a medium-pressure preheater, a low-pressure vaporizer and a low-pressure preheater. Furthermore, in some cases, it is worth heating the steam emerging from the medium-pressure section of the steam turbine in an intermediate superheater, before it is combined with the steam from the low-pressure superheater.
Overall, so much heat can be extracted from the exhaust gas from the gas turbine in the steam generator that its temperature when it emerges from the steam generator is actually less than 100xc2x0 C.
According to the invention, all the compressors may have approximately the same compression power. The heating power for heating the combustion air in the air preheater may also be approximately equal to five-times the cooling power in the air/water heat exchanger or exchangers. In this case, the heating power introduced by the exhaust gas into the medium-pressure steam generator and into the low-pressure steam generator may be virtually twice as great as the heating power in the air preheater.
Gas and steam turbine systems configured according to the invention are highly advantageous since they achieve approximately the same efficiency as, or greater efficiency than conventional systems, using a two-pressure steam turbine system. In particular, it is possible to dispense with the use of particularly expensive special materials for the steam generator and the steam turbine. This is achieved, for example, by the low inlet temperatures of the hot gas, in particular of the burnt gas, into the gas turbine which are possible. Furthermore, the construction and the circuit of the new systems are also relatively simple, so that maintenance can be carried out by personnel with average training.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a gas and steam turbine system, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.